So in the meantime, going back now a couple of months, there was a meeting of all the leading physicists at Pocono in the spring of '48, where I wasn't invited but there were then all the leading people, Schwinger and Feynman and Bethe and Oppenheimer and Niels Bohr and Rabi and Lamb, all those people were there. And that was where Schwinger then presented his new version of quantum electrodynamics, which was also getting the right answers. Schwinger had in fact been able to calculate the magnetic moment of the electron and get the right answer, which was a great triumph. That was another of the Columbian experiments done by Kusch and Foley, where they measured the magnetic moment of the electron very precisely, and they found that it was not the Dirac value, but differed from the Dirac value by a certain finite amount, which then Schwinger was able to calculate. And then - so that was a big triumph for Schwinger - and his method of calculating was much more conventional. It was essentially just a relativistic version of Hans Bethe's method. It involved things that Schwinger called Green's Functions, which again I found rather incomprehensible, but Schwinger was very obscure when he described the things he was doing. He loved to make the - as Oppenheimer said, most people when they explain something, they're telling you how to do it; but when Schwinger explains something he's telling you that only he can do it! That was roughly the way it was, I mean, so from Schwinger one only had the impression that this was so difficult and so elaborate a way of calculating, only Schwinger could possibly do it. So people were not too happy with that. But then later on Feynman also was able to calculate the electromagnetic moment and he also got the right answer with his completely different method. So that was also very impressive, that both of these methods somehow must be doing the same thing in some fashion, but nobody understood really the connection. So that was the background in which I came to Ann Arbor; and in Ann Arbor in June of '48 I learned the stuff from Schwinger himself. I listened to his lectures in the morning and I spent the afternoons working very hard, just simply going through the Schwinger lectures step by step and really understanding what he'd been saying, which was very hard work because he just had this wonderfully baroque style of lecturing in which everything was dressed up to be as complicated as possible, and the answer somehow came out miraculously at the end. But I managed to figure out what he'd been doing, so what was clear at the end of this was that actually the Green's Functions that Schwinger was using were really the same thing as the commutators in quantum field theory, that in a way what Schwinger was doing was basically quantum field theory, and that was something I knew, because I'd had it from Kemmer, so I was able to translate Schwinger into the language of quantum field theory and that made sense of it. And then the problem remained whether one could connect that with Feynman, whether one could reduce Feynman also to quantum field theory, and that remained a problem after I finished at Ann Arbor. It was clearly the next thing I had to try. And you actually could talk to Schwinger, I mean... I talked with him very well, in a very happy way. I mean Schwinger was actually very friendly to me.

[Q] And very approachable on a one to one..?

Yes. When I had him alone, I mean, all this public performance, this disappeared. He actually told me quite plainly what he was doing. No, he was very pleasant, and I always felt he was really a great gentleman because afterwards I sort of stole his thunder, and he never made any complaints.

Born in England in 1923, Freeman Dyson moved to Cornell University after graduating from Cambridge University with a BA in Mathematics. He subsequently became a professor and worked on nuclear reactors, solid state physics, ferromagnetism, astrophysics and biology. He has published several books and, among other honours, has been awarded the Heineman Prize and the Royal Society's Hughes Medal.

Silvan Sam Schweber is the Koret Professor of the History of Ideas and Professor of Physics at Brandeis University, and a Faculty Associate in the Department of the History of Science at Harvard University. He is the author of a history of the development of quantum electro mechanics, "QED and the men who made it", and has recently completed a biography of Hans Bethe and the history of nuclear weapons development, "In the Shadow of the Bomb: Oppenheimer, Bethe, and the Moral Responsibility of the Scientist" (Princeton University Press, 2000).